Catalyst component for reducing the total acid number in refinery feedstocks

ABSTRACT

A catalyst component is described for reducing the total acid number of a refinery feedstock. A solid catalyst material that is pretreated with a caustic base solution form the catalyst component effective for contacting a refinery feedstock to reduce the total acid number.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 61/513,042 filed Jul. 29, 2011, the disclosure of whichis hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to upgrading refinery feedstocks, inparticular to reduce the total acid number by neutralizing naphthenicacids.

Description of Related Art

Compositions of natural petroleum or crude oils vary significantly basedon numerous factors, mainly the geographic source, and even within aparticular region, the composition can vary. Common to virtually allsources of crude oil is the existence of heteroatoms such as sulfur,nitrogen, nickel, vanadium and others. Some crude oils also containnaphthenic acid compounds. These impurities are present in quantitiesthat impact the refinery processing of the crude oil and its fractions.

The term “naphthenic acid” is derived from the first observation of theacidity in naphthenic-based crude. The chemical compositions ofnaphthenic acids are extremely complex, and a great variety ofstructures and compositions fall within the classification of naphthenicacids. Naphthenic acids are predominantly made up of carboxyliccycloaliphatic acids substituted with alkyl, with lower proportions ofnon-cycloaliphatic acids. Aromatic, olefinic, hydroxylic and dibasicacids may be present as minor components. The molecular weight ofnaphthenic acids present in crude oils, as determined by massspectrometry, varies generally between about 120 and more than 700 gramsper mole. Presence of naphthenic acid compounds contributes to theacidity of crude oils and is one of the major causes of corrosion in oilpipelines and distillation units in oil refineries. Consequently, crudeoils with high naphthenic acid concentrations are considered to be ofpoor quality and are marketed at a lower price.

Total acid number (“TAN”) is a commonly accepted criterion for the oilacidity, although its correlation with corrosive behavior is stilluncertain. Specifically, TAN represents the number of milligrams ofpotassium hydroxide required to neutralize the acidity of 1 gram of oil.Some crude oils possess extremely high levels of naphthenic acidity(e.g., oils which would require between 3 and 10 milligrams of potassiumhydroxide per gram of oil in order to neutralize such acidity), and donot meet current material specifications of refineries. Metallurgicadequacy of industrial units is obtained by substituting equipment,metal pipes, etc., and is a function of naphthenic acid distribution inthe oil fractions, which are subject to change in processing oils comingfrom new reservoirs.

The high acid content also influences the value and marketability ofcrude oil. For example, currently the market value is discounted forcrude oil having a TAN greater than 0.5 milligrams potassium hydroxideper gram of oil.

Moreover, the polarized character of carboxyls promotes the formation ofemulsions, especially in heavier hydrocarbon feedstocks. This reducesthe efficiency of the desalination stage of petroleum, making theseparation of the water/oil emulsions difficult. Therefore, high aciditynot only reduces market value, but adversely affects the refiningprocess.

Reducing TAN from refinery feedstocks is regarded as one of the mostimportant processes in heavy oil upgrading. One approach is to mixfeedstock having a relatively high TAN with a feedstock having arelatively low TAN. However, the acidic compounds remain in the blendedfeedstock, and the higher market value low TAN hydrocarbon feedstock issacrificed. Other methods include washing a feedstock with a causticsolution. This treatment can remove naphthenic acids, but the processgenerates significant amount of wastewater and emulsions that aredifficult to treat. Further approaches include adsorption of thenaphthenic acid through adsorbent compounds with or without catalyticproperties or contacting with other catalysts, including hydrotreatingcatalysts.

Nonetheless, a need remains in the industry for improved processes fortreatment of refinery feedstocks to reduce the TAN, neutralizenaphthenic acids, and/or break or prevent the formation of emulsions, inan efficient and economically feasible manner.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to efficiently andeconomically reduce the TAN of a hydrocarbon feedstock containingnaphthenic acids.

Another object of the present invention is to reduce the TAN whilebreaking emulsions or minimizing or preventing the likelihood of theirformation.

In accordance with one or more embodiments, a process for reducing theTAN of a refinery feedstock containing naphthenic acids is provided. Therefinery feedstock containing naphthenic acids is contacted with aneffective amount of solid heterogeneous catalyst in the presence of anaqueous base for a period of time sufficient to neutralize at least aportion of the naphthenic acids in the feedstock to produce a treatedmixture. The mixture is phase separated into an aqueous phase and aneutralized hydrocarbon phase.

In accordance with one or more additional embodiments, the processcomprises contacting the hydrocarbon feedstock containing naphthenicacids with an effective amount of solid catalyst that has beenpretreated with a caustic base for a period of time sufficient toneutralize at least a portion of the naphthenic acids in the hydrocarbonfeedstock to produce a treated hydrocarbon feedstock having reducedamount of naphthenic acids.

Still other aspects, embodiments, and advantages of these exemplaryaspects and embodiments, are discussed in detail below. Moreover, it isto be understood that both the foregoing information and the followingdetailed description are merely illustrative examples of various aspectsand embodiments, and are intended to provide an overview or frameworkfor understanding the nature and character of the claimed aspects andembodiments. The accompanying drawing is included to provideillustration and a further understanding of the various aspects andembodiments, and is incorporated in and constitutes a part of thisspecification. The drawing, together with the remainder of thespecification, serves to explain principles and operations of thedescribed and claimed aspects and embodiments.

BRIEF DESCRIPTION OF THE DRAWING

The foregoing summary as well as the following detailed description willbe best understood when read in conjunction with the attached drawing.It should be understood, however, that the invention is not limited tothe precise arrangements and apparatus shown.

FIG. 1 is a process flow diagram of a system for reducing the TAN of arefinery feedstock.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a system 10 for reducing the TAN of a refineryfeedstock is schematically illustrated. Details such as pumps,instrumentations, heat exchangers, boilers, compressors, and similarhardware have been omitted as being non-essential to understand thetechniques involved in this invention. System 10 includes aneutralization vessel 4 and a separator drum 6. Neutralization vessel 4includes an inlet 3 for receiving a hydrocarbon feedstock via conduit 1and an aqueous caustic base via conduit 2, and an outlet 5 fordischarging a treated mixture. Separator drum 6 includes an inlet 11 forreceiving the treated mixture, an outlet 7 for discharging a neutralizedhydrocarbon feedstock, an outlet 8 for discharging an aqueous phase, andan outlet 9 for discharging light gases. In certain embodiments,emulsion breaking additives can be incorporated in separator drum 6,e.g., via conduit 12 (shown in dashed lines).

In the practice of the system described herein, a hydrocarbon feedstockcontaining naphthenic acids introduced via conduit 1 is mixed with anaqueous caustic base introduced via conduit 2. The mixture is charged tothe neutralization vessel 4 via inlet 3. Neutralization vessel 4contains a single catalyst or a group of catalysts. The mixture isbrought into contact with the catalyst and maintained in contact for asufficient period of time to neutralize naphthenic acid compoundspresent in the hydrocarbon feedstock. The treated mixture is dischargedvia outlet 5 and passed to separator drum 6 via inlet 11.

The treated mixture is separated into three portions: a neutralizedhydrocarbon feedstock having a reduced TAN by neutralization ofnaphthenic acids, which is recovered as product via outlet 7; an aqueousphase containing spent caustic base discharged via outlet 8; and lightgases including H₂S, NH₃ and light hydrocarbon gases (e.g., havingcarbon numbers between 1 and 4) discharged via outlet 9.

In an additional embodiment the catalyst material contained inneutralization vessel is pretreated with a caustic base, such as sodiumhydroxide or potassium hydroxide. In this embodiment, the caustic baseand separator drum are not present.

The pretreatment of catalyst can be in situ (e.g., in a neutralizationvessel) or ex situ (e.g., in a continuous tubular vessel or batchequipment). In an exemplary embodiment of in situ catalyst preparation,an alumina base catalyst is loaded into the neutralization vessel, and a50 weight % caustic base solution is heated to 320° C. and fed throughthe catalyst bed at a liquid hourly space velocity of 0.3 h⁻¹ for 5 to10 hours. After catalyst pretreatment, feedstock can be charged forneutralization of naphthenic acids. In an exemplary embodiment of exsitu preparation, an alumina catalyst in pellet form is heated to 320°C. in a batch vessel and then mixed with a 50 weight % caustic basesolution for 3 hours. The caustic base solution is drained and the solidcatalyst particles are dried and loaded into the neutralization vessel.

The refinery feedstock for use in above-described apparatus and processcan be a crude or partially refined or fractions of hydrocarbon productobtained from various sources. The source of the refinery feedstock canbe naturally occurring crude oil, synthetic crude oil, bitumen, oilsand, shale oil, coal liquids, or a combination including one of theforegoing sources. For example, the feedstock can be naphtha, gas oil,vacuum gas oil or other refinery intermediate stream such as vacuum gasoil, deasphalted oil and/or demetalized oil obtained from a solventdeasphalting process, light coker or heavy coker gas oil obtained from acoker process, cycle oil obtained from an FCC process, gas oil obtainedfrom a visbreaking process, or any combination of the foregoingproducts. Nonetheless, one of ordinary skill in the art will appreciatethat other hydrocarbon streams can benefit from the practice of theherein described system and method.

The aqueous caustic base can be sodium hydroxide or potassium hydroxide.In certain embodiments, the amount of caustic base supplied throughconduit 2 is in the range of from 0.05 to 30 weight % based on theweight of the catalyst.

Neutralization vessel 4 can be a fixed, moving, fluidized, or swing bedsystem. In certain embodiments a fixed bed reactor is suitable. Ingeneral, the operating conditions of the neutralization vessel include apressure in the range of from 1 to 20 Kg/cm², in certain embodimentsfrom 1 to 10 Kg/cm²; a temperature in the range of from 200° C. to 600°C., in certain embodiments from 300° C. to 400° C., and in furtherembodiments from 300° C. to 350° C.; and a liquid hourly space velocityof the refinery feedstock in the range of from 0.1 to 10 h⁻¹, in certainembodiments from 0.5 to 4 h⁻¹, and in further embodiments from 1 to 2h⁻¹. In certain embodiments, pressure within the neutralization vesselcan be maintained by the hydrocarbon pressure alone, without any supplyof added overhead or blanketing gas.

The neutralization vessel contains catalysts having basic properties. Incertain embodiments the catalyst comprises at least one metal oxideselected from the group consisting of zinc oxide, aluminum oxide, zincaluminates, and layered double hydroxides including magnesium/aluminum.The catalyst is in the form of pellets, spheres, or any other suitableshape. Generally, catalyst particle size and shape are chosen, as isknown in the art, in such a manner as to prevent undue pressure dropacross the bed, yet permit adequate diffusion of reactants to activesites on the catalyst surface of within the catalyst particle.

In certain embodiments, demulsifier additives can be added to separatordrum 6 to efficiently separate oil and water. These emulsion breakingadditives may be selected from the group consisting of triethanolamine,ethoxylated phenol resins, zinc chloride and polymerizedtrithionylamine.

The process described herein can be conducted at various stages inrefinery operations or upstream. For instance, the process can beimplemented to treat influent feedstock in a refinery or fractionsthereof. In alternative embodiments, the process can be implementedupstream of or within a gas oil separation plant, for instance,downstream of desalting stages.

The method and system herein have been described above and in theattached drawing; however, modifications will be apparent to those ofordinary skill in the art and the scope of protection for the inventionis to be defined by the claims that follow.

1-31. (canceled)
 32. A catalyst component for reducing the total acidnumber of a refinery feedstock containing naphthenic acids comprisingone or more solid catalyst materials selected from the group consistingof zinc aluminates and layered double hydroxides includingmagnesium/aluminum, wherein the solid catalyst material is pretreatedwith an aqueous caustic base prior to use.
 33. The catalyst component ofclaim 32, wherein the aqueous caustic base comprises sodium hydroxide orpotassium hydroxide.
 34. The catalyst component of claim 32, wherein thecolic catalyst material is pretreated in situ h contacting with theaqueous caustic base in a neutralization vessel used for contacting arefinery feedstock.
 35. The catalyst component of claim 32, wherein thesolid catalyst material is pretreated ex situ by contacting with theaqueous caustic base in a vessel separate from a neutralization vesselused for contacting a refinery feedstock.
 36. (canceled)
 37. (canceled)38. (canceled)
 39. (canceled)
 40. The catalyst component of claim 32,wherein the solid catalyst comprises zinc aluminates.
 41. The catalystcomponent of claim 32, wherein the solid catalyst comprises layereddouble hydroxides including magnesium/aluminum.